Pen



FIG. 1 is a side perspective view of a design for a pen according to the present invention;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is an exploded view of the pen of FIG. 1. 

CLAIM The ornamental design for a pen, as shown and described. 